To elucidate the processes that have been industrially employed from long ago at the atomic and molecular level is becoming more important with regard to new energy resources. This has become possible with the invention of scanning tunneling microscopy (STM) which allows observation at the atomic level. The inventors of STM won the Nobel Prize in 1986. Since then, more advanced scanning probe microscopy (SPM) techniques have been developed and it has become possible to investigate not only the surface morphology but also physical and chemical properties using various probes. In 1989, A. J. Bard et al. proposed a scanning electrochemical microscopy (SECM) technique using a small and movable electrochemical probe called an ultramicroelectrode (UME) as a new-concept probe. Since it enables not only observation of the surface morphology but also monitoring the electrochemical reactions occurring on the surface, it is widely used in electrochemical researches on various interfaces.
The probe having microscopic spatial resolution is useful in finding out surface defects resulting from chemical reactions occurring on interfaces such as corrosion or dissolution. Also, it is useful in developing new catalyst materials since it allows fast evaluation of many materials having catalytic activity. For example, development of a new catalyst material for effectively improving the performance of a fuel cell which converts the chemical energy from a fuel into electricity is industrially invaluable since it can replace the expensive platinum catalyst. In addition, the probe may be used to investigate the mechanism and rate of reactions occurring on interfaces. Accordingly, by establishing the condition of ideal catalyst materials through studies on the mechanism of various catalytic reactions, the SECM technique will provide a basis for systematic catalyst development, beyond the existing catalyst development based on limited information.
However, the problems including limitation only to electrochemically active materials, applicability only to materials that can be desorbed from the electrode surface and diffuse into the solution phase, failure to provide information other than electrochemical data, or the like have greatly limited the application of SECM industrially and the SECM technique remains only as a research tool. If the SECM technique can be improved into a system capable of providing chemical information of materials involved in electrochemical reactions in real time, it will be used in various applications. The best way to achieve it is to develop a probe capable of providing not only electrochemical information but also spectroscopic information. The existing SECM probe provides electrochemical information only and cannot provide information about intermediates present on the surface. However, considering that most electrochemical reactions occur in water, spectroscopic measurement is extremely restricted due to absorption by water itself. Raman spectroscopy is one of few methods that can be used in water without a special device and it can be widely used to provide chemical information about electrochemical reactions. However, because the signals from Raman spectroscopic measurement are usually very weak in intensity, only the surface-enhanced Raman scattering (SERS) technique is practically applicable. The SERS phenomenon is found only in specific materials and structures and it is impossible to obtain Raman spectra for electrochemical reactions occurring on electrodes made of arbitrary materials. If a device capable of obtaining Raman spectra, regardless of the material of the electrode on which an electrochemical reaction of interest is occurring, is coupled with the existing SECM technique, it will make a useful analysis tool in many applications including catalyst development.